@@ -1,151 +1,95 @@
1−{-# LANGUAGE CPP #-}
21{-# LANGUAGE DeriveTraversable #-}
32{-# LANGUAGE FlexibleContexts #-}
43{-# LANGUAGE FlexibleInstances #-}
5−{-# LANGUAGE GeneralizedNewtypeDeriving #-}
64{-# LANGUAGE LambdaCase #-}
75{-# LANGUAGE MultiParamTypeClasses #-}
86{-# LANGUAGE PatternGuards #-}
9−{-# LANGUAGE PatternSynonyms #-}
107{-# LANGUAGE ScopedTypeVariables #-}
11−{-# LANGUAGE StandaloneDeriving #-}
128{-# LANGUAGE TemplateHaskell #-}
139{-# LANGUAGE TypeApplications #-}
1410{-# LANGUAGE TypeFamilies #-}
15−{-# LANGUAGE ViewPatterns #-}
1611
1712-- | 'Patch'es on 'Map' that can insert, delete, and move values from one key to
1813-- another
19−module Data.Patch.MapWithMove
20− ( PatchMapWithMove
21− ( PatchMapWithMove
22− , unPatchMapWithMove
23− , ..
24− )
25− , patchMapWithMove
26− , patchMapWithMoveInsertAll
27− , insertMapKey
28− , moveMapKey
29− , swapMapKey
30− , deleteMapKey
31− , unsafePatchMapWithMove
32− , patchMapWithMoveNewElements
33− , patchMapWithMoveNewElementsMap
34− , patchThatSortsMapWith
35− , patchThatChangesAndSortsMapWith
36− , patchThatChangesMap
14+module Data.Patch.MapWithMove where
3715
38− -- * Node Info
39− , NodeInfo
40− ( NodeInfo
41− , _nodeInfo_to
42− , _nodeInfo_from
43− , ..
44− )
45− , bitraverseNodeInfo
46− , nodeInfoMapFrom
47− , nodeInfoMapMFrom
48− , nodeInfoSetTo
49−
50− -- * From
51− , From
52− ( From_Insert
53− , From_Delete
54− , From_Move
55− , ..
56− )
57− , bitraverseFrom
58−
59− -- * To
60− , To
61− ) where
62−
63−import Data.Coerce
64−import Data.Kind (Type)
6516import Data.Patch.Class
66−import Data.Patch.MapWithPatchingMove (PatchMapWithPatchingMove(..), To)
67−import qualified Data.Patch.MapWithPatchingMove as PM -- already a transparent synonym
6817
69−import Control.Lens
18+import Control.Arrow
19+import Control.Lens hiding (from, to)
20+import Control.Monad.Trans.State
21+import Data.Foldable
22+import Data.Function
7023import Data.List
7124import Data.Map (Map)
7225import qualified Data.Map as Map
73−import Data.Proxy
74−#if !MIN_VERSION_base(4,11,0)
75−import Data.Semigroup (Semigroup (..))
76−#endif
77−import Data.Traversable (foldMapDefault)
26+import Data.Maybe
27+import Data.Semigroup (Semigroup (..), (<>))
28+import qualified Data.Set as Set
29+import Data.These (These(..))
30+import Data.Tuple
7831
7932-- | Patch a Map with additions, deletions, and moves. Invariant: If key @k1@
8033-- is coming from @From_Move k2@, then key @k2@ should be going to @Just k1@,
8134-- and vice versa. There should never be any unpaired From/To keys.
82−newtype PatchMapWithMove k (v :: Type) = PatchMapWithMove'
83− { -- | Extract the underlying 'PatchMapWithPatchingMove k (Proxy v)'
84− unPatchMapWithMove' :: PatchMapWithPatchingMove k (Proxy v)
35+newtype PatchMapWithMove k v = PatchMapWithMove
36+ { -- | Extract the internal representation of the 'PatchMapWithMove'
37+ unPatchMapWithMove :: Map k (NodeInfo k v)
8538 }
8639 deriving ( Show, Read, Eq, Ord
87−-- Haddock cannot handle documentation here before GHC 8.6
88− ,
89−#if __GLASGOW_HASKELL__ >= 806
90− -- | Compose patches having the same effect as applying the
91− -- patches in turn: @'applyAlways' (p <> q) == 'applyAlways' p .
92− -- 'applyAlways' q@
93−#endif
94− Semigroup
95− , Monoid
40+ , Functor, Foldable, Traversable
9641 )
9742
98−pattern Coerce :: Coercible a b => a -> b
99−pattern Coerce x <- (coerce -> x)
100− where Coerce x = coerce x
101−
102−{-# COMPLETE PatchMapWithMove #-}
103−pattern PatchMapWithMove :: Map k (NodeInfo k v) -> PatchMapWithMove k v
104−-- | Extract the representation of the 'PatchMapWithMove' as a map of
105−-- 'NodeInfo'.
106−unPatchMapWithMove :: PatchMapWithMove k v -> Map k (NodeInfo k v)
107−pattern PatchMapWithMove { unPatchMapWithMove } = PatchMapWithMove' (PatchMapWithPatchingMove (Coerce unPatchMapWithMove))
108−
109−_PatchMapWithMove
110− :: Iso
111− (PatchMapWithMove k0 v0)
112− (PatchMapWithMove k1 v1)
113− (Map k0 (NodeInfo k0 v0))
114− (Map k1 (NodeInfo k1 v1))
115−_PatchMapWithMove = iso unPatchMapWithMove PatchMapWithMove
43+-- | Holds the information about each key: where its new value should come from,
44+-- and where its old value should go to
45+data NodeInfo k v = NodeInfo
46+ { _nodeInfo_from :: !(From k v)
47+ -- ^ Where do we get the new value for this key?
48+ , _nodeInfo_to :: !(To k)
49+ -- ^ If the old value is being kept (i.e. moved rather than deleted or
50+ -- replaced), where is it going?
51+ }
52+ deriving (Show, Read, Eq, Ord, Functor, Foldable, Traversable)
11653
117−instance Functor (PatchMapWithMove k) where
118− fmap f = runIdentity . traverse (Identity . f)
54+-- | Describe how a key's new value should be produced
55+data From k v
56+ = From_Insert v -- ^ Insert the given value here
57+ | From_Delete -- ^ Delete the existing value, if any, from here
58+ | From_Move !k -- ^ Move the value here from the given key
59+ deriving (Show, Read, Eq, Ord, Functor, Foldable, Traversable)
11960
120−instance Foldable (PatchMapWithMove k) where
121− foldMap = foldMapDefault
61+-- | Describe where a key's old value will go. If this is 'Just', that means
62+-- the key's old value will be moved to the given other key; if it is 'Nothing',
63+-- that means it will be deleted.
64+type To = Maybe
12265
123−instance Traversable (PatchMapWithMove k) where
124− traverse =
125− _PatchMapWithMove .
126− traverse .
127− traverse
66+makeWrapped ''PatchMapWithMove
12867
12968instance FunctorWithIndex k (PatchMapWithMove k)
13069instance FoldableWithIndex k (PatchMapWithMove k)
13170instance TraversableWithIndex k (PatchMapWithMove k) where
132− itraverse = itraversed . Indexed
133− itraversed =
134− _PatchMapWithMove .>
135− itraversed <.
136− traverse
71+ itraverse f (PatchMapWithMove x) = PatchMapWithMove <$> itraverse (traverse . f) x
13772
13873-- | Create a 'PatchMapWithMove', validating it
13974patchMapWithMove :: Ord k => Map k (NodeInfo k v) -> Maybe (PatchMapWithMove k v)
140−patchMapWithMove = fmap PatchMapWithMove' . PM.patchMapWithPatchingMove . coerce
75+patchMapWithMove m = if valid then Just $ PatchMapWithMove m else Nothing
76+ where valid = forwardLinks == backwardLinks
77+ forwardLinks = Map.mapMaybe _nodeInfo_to m
78+ backwardLinks = Map.fromList $ catMaybes $ flip fmap (Map.toList m) $ \(to, v) ->
79+ case _nodeInfo_from v of
80+ From_Move from -> Just (from, to)
81+ _ -> Nothing
14182
14283-- | Create a 'PatchMapWithMove' that inserts everything in the given 'Map'
14384patchMapWithMoveInsertAll :: Map k v -> PatchMapWithMove k v
144−patchMapWithMoveInsertAll = PatchMapWithMove' . PM.patchMapWithPatchingMoveInsertAll
85+patchMapWithMoveInsertAll m = PatchMapWithMove $ flip fmap m $ \v -> NodeInfo
86+ { _nodeInfo_from = From_Insert v
87+ , _nodeInfo_to = Nothing
88+ }
14589
14690-- | Make a @'PatchMapWithMove' k v@ which has the effect of inserting or updating a value @v@ to the given key @k@, like 'Map.insert'.
14791insertMapKey :: k -> v -> PatchMapWithMove k v
148−insertMapKey k v = PatchMapWithMove' $ PM.insertMapKey k v
92+insertMapKey k v = PatchMapWithMove . Map.singleton k $ NodeInfo (From_Insert v) Nothing
14993
15094-- |Make a @'PatchMapWithMove' k v@ which has the effect of moving the value from the first key @k@ to the second key @k@, equivalent to:
15195--
@@ -153,53 +97,84 @@ insertMapKey k v = PatchMapWithMove' $ PM.insertMapKey k v
15397-- 'Map.delete' src (maybe map ('Map.insert' dst) (Map.lookup src map))
15498-- @
15599moveMapKey :: Ord k => k -> k -> PatchMapWithMove k v
156−moveMapKey src dst = PatchMapWithMove' $ PM.moveMapKey src dst
100+moveMapKey src dst
101+ | src == dst = mempty
102+ | otherwise =
103+ PatchMapWithMove $ Map.fromList
104+ [ (dst, NodeInfo (From_Move src) Nothing)
105+ , (src, NodeInfo From_Delete (Just dst))
106+ ]
157107
158108-- |Make a @'PatchMapWithMove' k v@ which has the effect of swapping two keys in the mapping, equivalent to:
159109--
160110-- @
161111-- let aMay = Map.lookup a map
162112-- bMay = Map.lookup b map
163−-- in maybe id (Map.insert a) (bMay <> aMay)
164−-- . maybe id (Map.insert b) (aMay <> bMay)
113+-- in maybe id (Map.insert a) (bMay `mplus` aMay)
114+-- . maybe id (Map.insert b) (aMay `mplus` bMay)
165115-- . Map.delete a . Map.delete b $ map
166116-- @
167117swapMapKey :: Ord k => k -> k -> PatchMapWithMove k v
168−swapMapKey src dst = PatchMapWithMove' $ PM.swapMapKey src dst
118+swapMapKey src dst
119+ | src == dst = mempty
120+ | otherwise =
121+ PatchMapWithMove $ Map.fromList
122+ [ (dst, NodeInfo (From_Move src) (Just src))
123+ , (src, NodeInfo (From_Move dst) (Just dst))
124+ ]
169125
170126-- |Make a @'PatchMapWithMove' k v@ which has the effect of deleting a key in the mapping, equivalent to 'Map.delete'.
171127deleteMapKey :: k -> PatchMapWithMove k v
172−deleteMapKey = PatchMapWithMove' . PM.deleteMapKey
128+deleteMapKey k = PatchMapWithMove . Map.singleton k $ NodeInfo From_Delete Nothing
173129
174130-- | Wrap a @'Map' k (NodeInfo k v)@ representing patch changes into a @'PatchMapWithMove' k v@, without checking any invariants.
175131--
176132-- __Warning:__ when using this function, you must ensure that the invariants of 'PatchMapWithMove' are preserved; they will not be checked.
177133unsafePatchMapWithMove :: Map k (NodeInfo k v) -> PatchMapWithMove k v
178−unsafePatchMapWithMove = coerce PM.unsafePatchMapWithPatchingMove
134+unsafePatchMapWithMove = PatchMapWithMove
179135
180136-- | Apply the insertions, deletions, and moves to a given 'Map'
181137instance Ord k => Patch (PatchMapWithMove k v) where
182138 type PatchTarget (PatchMapWithMove k v) = Map k v
183− apply (PatchMapWithMove' p) = apply p
139+ apply (PatchMapWithMove p) old = Just $! insertions `Map.union` (old `Map.difference` deletions) --TODO: return Nothing sometimes --Note: the strict application here is critical to ensuring that incremental merges don't hold onto all their prerequisite events forever; can we make this more robust?
140+ where insertions = flip Map.mapMaybeWithKey p $ \_ ni -> case _nodeInfo_from ni of
141+ From_Insert v -> Just v
142+ From_Move k -> Map.lookup k old
143+ From_Delete -> Nothing
144+ deletions = flip Map.mapMaybeWithKey p $ \_ ni -> case _nodeInfo_from ni of
145+ From_Delete -> Just ()
146+ _ -> Nothing
184147
185148-- | Returns all the new elements that will be added to the 'Map'.
186149patchMapWithMoveNewElements :: PatchMapWithMove k v -> [v]
187−patchMapWithMoveNewElements = PM.patchMapWithPatchingMoveNewElements . unPatchMapWithMove'
150+patchMapWithMoveNewElements = Map.elems . patchMapWithMoveNewElementsMap
188151
189152-- | Return a @'Map' k v@ with all the inserts/updates from the given @'PatchMapWithMove' k v@.
190153patchMapWithMoveNewElementsMap :: PatchMapWithMove k v -> Map k v
191−patchMapWithMoveNewElementsMap = PM.patchMapWithPatchingMoveNewElementsMap . unPatchMapWithMove'
154+patchMapWithMoveNewElementsMap (PatchMapWithMove p) = Map.mapMaybe f p
155+ where f ni = case _nodeInfo_from ni of
156+ From_Insert v -> Just v
157+ From_Move _ -> Nothing
158+ From_Delete -> Nothing
192159
193160-- | Create a 'PatchMapWithMove' that, if applied to the given 'Map', will sort
194161-- its values using the given ordering function. The set keys of the 'Map' is
195162-- not changed.
196163patchThatSortsMapWith :: Ord k => (v -> v -> Ordering) -> Map k v -> PatchMapWithMove k v
197−patchThatSortsMapWith cmp = PatchMapWithMove' . PM.patchThatSortsMapWith cmp
164+patchThatSortsMapWith cmp m = PatchMapWithMove $ Map.fromList $ catMaybes $ zipWith g unsorted sorted
165+ where unsorted = Map.toList m
166+ sorted = sortBy (cmp `on` snd) unsorted
167+ f (to, _) (from, _) = if to == from then Nothing else
168+ Just (from, to)
169+ reverseMapping = Map.fromList $ catMaybes $ zipWith f unsorted sorted
170+ g (to, _) (from, _) = if to == from then Nothing else
171+ let Just movingTo = Map.lookup to reverseMapping
172+ in Just (to, NodeInfo (From_Move from) $ Just movingTo)
198173
199174-- | Create a 'PatchMapWithMove' that, if applied to the first 'Map' provided,
200175-- will produce a 'Map' with the same values as the second 'Map' but with the
201176-- values sorted with the given ordering function.
202−patchThatChangesAndSortsMapWith :: (Ord k, Ord v) => (v -> v -> Ordering) -> Map k v -> Map k v -> PatchMapWithMove k v
177+patchThatChangesAndSortsMapWith :: forall k v. (Ord k, Ord v) => (v -> v -> Ordering) -> Map k v -> Map k v -> PatchMapWithMove k v
203178patchThatChangesAndSortsMapWith cmp oldByIndex newByIndexUnsorted = patchThatChangesMap oldByIndex newByIndex
204179 where newList = Map.toList newByIndexUnsorted
205180 newByIndex = Map.fromList $ zip (fst <$> newList) $ sortBy cmp $ snd <$> newList
@@ -207,106 +182,102 @@ patchThatChangesAndSortsMapWith cmp oldByIndex newByIndexUnsorted = patchThatCha
207182-- | Create a 'PatchMapWithMove' that, if applied to the first 'Map' provided,
208183-- will produce the second 'Map'.
209184patchThatChangesMap :: (Ord k, Ord v) => Map k v -> Map k v -> PatchMapWithMove k v
210−patchThatChangesMap oldByIndex newByIndex = PatchMapWithMove' $
211− PM.patchThatChangesMap oldByIndex newByIndex
212−
213−--
214−-- NodeInfo
215−--
216−
217−-- | Holds the information about each key: where its new value should come from,
218−-- and where its old value should go to
219−newtype NodeInfo k (v :: Type) = NodeInfo' { unNodeInfo' :: PM.NodeInfo k (Proxy v) }
220−
221−deriving instance (Show k, Show p) => Show (NodeInfo k p)
222−deriving instance (Read k, Read p) => Read (NodeInfo k p)
223−deriving instance (Eq k, Eq p) => Eq (NodeInfo k p)
224−deriving instance (Ord k, Ord p) => Ord (NodeInfo k p)
225−
226−{-# COMPLETE NodeInfo #-}
227−pattern NodeInfo :: To k -> From k v -> NodeInfo k v
228−_nodeInfo_to :: NodeInfo k v -> To k
229−_nodeInfo_from :: NodeInfo k v -> From k v
230−pattern NodeInfo { _nodeInfo_to, _nodeInfo_from } = NodeInfo'
231− PM.NodeInfo
232− { PM._nodeInfo_to = _nodeInfo_to
233− , PM._nodeInfo_from = Coerce _nodeInfo_from
234− }
235−
236−_NodeInfo
237− :: Iso
238− (NodeInfo k0 v0)
239− (NodeInfo k1 v1)
240− (PM.NodeInfo k0 (Proxy v0))
241− (PM.NodeInfo k1 (Proxy v1))
242−_NodeInfo = iso unNodeInfo' NodeInfo'
243−
244−instance Functor (NodeInfo k) where
245− fmap f = runIdentity . traverse (Identity . f)
246−
247−instance Foldable (NodeInfo k) where
248− foldMap = foldMapDefault
249−
250−instance Traversable (NodeInfo k) where
251− traverse = bitraverseNodeInfo pure
252−
253−bitraverseNodeInfo
254− :: Applicative f
255− => (k0 -> f k1)
256− -> (v0 -> f v1)
257− -> NodeInfo k0 v0 -> f (NodeInfo k1 v1)
258−bitraverseNodeInfo fk fv = fmap NodeInfo'
259− . PM.bitraverseNodeInfo fk (\ ~Proxy -> pure Proxy) fv
260− . coerce
185+patchThatChangesMap oldByIndex newByIndex = patch
186+ where oldByValue = Map.fromListWith Set.union $ swap . first Set.singleton <$> Map.toList oldByIndex
187+ (insertsAndMoves, unusedValuesByValue) = flip runState oldByValue $ do
188+ let f k v = do
189+ remainingValues <- get
190+ let putRemainingKeys remainingKeys = put $ if Set.null remainingKeys
191+ then Map.delete v remainingValues
192+ else Map.insert v remainingKeys remainingValues
193+ case Map.lookup v remainingValues of
194+ Nothing -> return $ NodeInfo (From_Insert v) $ Just undefined -- There's no existing value we can take
195+ Just fromKs ->
196+ if k `Set.member` fromKs
197+ then do
198+ putRemainingKeys $ Set.delete k fromKs
199+ return $ NodeInfo (From_Move k) $ Just undefined -- There's an existing value, and it's here, so no patch necessary
200+ else do
201+ (fromK, remainingKeys) <- return . fromJust $ Set.minView fromKs -- There's an existing value, but it's not here; move it here
202+ putRemainingKeys remainingKeys
203+ return $ NodeInfo (From_Move fromK) $ Just undefined
204+ Map.traverseWithKey f newByIndex
205+ unusedOldKeys = fold unusedValuesByValue
206+ pointlessMove k = \case
207+ From_Move k' | k == k' -> True
208+ _ -> False
209+ keyWasMoved k = if k `Map.member` oldByIndex && not (k `Set.member` unusedOldKeys)
210+ then Just undefined
211+ else Nothing
212+ patch = unsafePatchMapWithMove $ Map.filterWithKey (\k -> not . pointlessMove k . _nodeInfo_from) $ Map.mergeWithKey (\k a _ -> Just $ nodeInfoSetTo (keyWasMoved k) a) (Map.mapWithKey $ \k -> nodeInfoSetTo $ keyWasMoved k) (Map.mapWithKey $ \k _ -> NodeInfo From_Delete $ keyWasMoved k) insertsAndMoves oldByIndex
261213
262214-- | Change the 'From' value of a 'NodeInfo'
263215nodeInfoMapFrom :: (From k v -> From k v) -> NodeInfo k v -> NodeInfo k v
264−nodeInfoMapFrom f = coerce $ PM.nodeInfoMapFrom (unFrom' . f . From')
216+nodeInfoMapFrom f ni = ni { _nodeInfo_from = f $ _nodeInfo_from ni }
265217
266218-- | Change the 'From' value of a 'NodeInfo', using a 'Functor' (or
267219-- 'Applicative', 'Monad', etc.) action to get the new value
268−nodeInfoMapMFrom
269− :: Functor f
270− => (From k v -> f (From k v))
271− -> NodeInfo k v -> f (NodeInfo k v)
272−nodeInfoMapMFrom f = fmap NodeInfo'
273− . PM.nodeInfoMapMFrom (fmap unFrom' . f . From')
274− . coerce
220+nodeInfoMapMFrom :: Functor f => (From k v -> f (From k v)) -> NodeInfo k v -> f (NodeInfo k v)
221+nodeInfoMapMFrom f ni = fmap (\result -> ni { _nodeInfo_from = result }) $ f $ _nodeInfo_from ni
275222
276223-- | Set the 'To' field of a 'NodeInfo'
277224nodeInfoSetTo :: To k -> NodeInfo k v -> NodeInfo k v
278−nodeInfoSetTo = coerce . PM.nodeInfoSetTo
279−
280−--
281−-- From
282−--
283−
284−-- | Describe how a key's new value should be produced
285−newtype From k (v :: Type) = From' { unFrom' :: PM.From k (Proxy v) }
286−
287−{-# COMPLETE From_Insert, From_Delete, From_Move #-}
288−
289−-- | Insert the given value here
290−pattern From_Insert :: v -> From k v
291−pattern From_Insert v = From' (PM.From_Insert v)
292−
293−-- | Delete the existing value, if any, from here
294−pattern From_Delete :: From k v
295−pattern From_Delete = From' PM.From_Delete
296−
297−-- | Move the value here from the given key
298−pattern From_Move :: k -> From k v
299−pattern From_Move k = From' (PM.From_Move k Proxy)
300−
301−bitraverseFrom
302− :: Applicative f
303− => (k0 -> f k1)
304− -> (v0 -> f v1)
305− -> From k0 v0 -> f (From k1 v1)
306−bitraverseFrom fk fv = fmap From'
307− . PM.bitraverseFrom fk (\ ~Proxy -> pure Proxy) fv
308− . coerce
309−
310−makeWrapped ''PatchMapWithMove
311−makeWrapped ''NodeInfo
312−makeWrapped ''From
225+nodeInfoSetTo to ni = ni { _nodeInfo_to = to }
226+
227+-- |Helper data structure used for composing patches using the monoid instance.
228+data Fixup k v
229+ = Fixup_Delete
230+ | Fixup_Update (These (From k v) (To k))
231+
232+-- |Compose patches having the same effect as applying the patches in turn: @'applyAlways' (p <> q) == 'applyAlways' p . 'applyAlways' q@
233+instance Ord k => Semigroup (PatchMapWithMove k v) where
234+ PatchMapWithMove ma <> PatchMapWithMove mb = PatchMapWithMove m
235+ where
236+ connections = Map.toList $ Map.intersectionWithKey (\_ a b -> (_nodeInfo_to a, _nodeInfo_from b)) ma mb
237+ h :: (k, (Maybe k, From k v)) -> [(k, Fixup k v)]
238+ h (_, (mToAfter, editBefore)) = case (mToAfter, editBefore) of
239+ (Just toAfter, From_Move fromBefore)
240+ | fromBefore == toAfter
241+ -> [(toAfter, Fixup_Delete)]
242+ | otherwise
243+ -> [ (toAfter, Fixup_Update (This editBefore))
244+ , (fromBefore, Fixup_Update (That mToAfter))
245+ ]
246+ (Nothing, From_Move fromBefore) -> [(fromBefore, Fixup_Update (That mToAfter))] -- The item is destroyed in the second patch, so indicate that it is destroyed in the source map
247+ (Just toAfter, _) -> [(toAfter, Fixup_Update (This editBefore))]
248+ (Nothing, _) -> []
249+ mergeFixups _ Fixup_Delete Fixup_Delete = Fixup_Delete
250+ mergeFixups _ (Fixup_Update a) (Fixup_Update b)
251+ | This x <- a, That y <- b
252+ = Fixup_Update $ These x y
253+ | That y <- a, This x <- b
254+ = Fixup_Update $ These x y
255+ mergeFixups _ _ _ = error "PatchMapWithMove: incompatible fixups"
256+ fixups = Map.fromListWithKey mergeFixups $ concatMap h connections
257+ combineNodeInfos _ nia nib = NodeInfo
258+ { _nodeInfo_from = _nodeInfo_from nia
259+ , _nodeInfo_to = _nodeInfo_to nib
260+ }
261+ applyFixup _ ni = \case
262+ Fixup_Delete -> Nothing
263+ Fixup_Update u -> Just $ NodeInfo
264+ { _nodeInfo_from = fromMaybe (_nodeInfo_from ni) $ getHere u
265+ , _nodeInfo_to = fromMaybe (_nodeInfo_to ni) $ getThere u
266+ }
267+ m = Map.differenceWithKey applyFixup (Map.unionWithKey combineNodeInfos ma mb) fixups
268+ getHere :: These a b -> Maybe a
269+ getHere = \case
270+ This a -> Just a
271+ These a _ -> Just a
272+ That _ -> Nothing
273+ getThere :: These a b -> Maybe b
274+ getThere = \case
275+ This _ -> Nothing
276+ These _ b -> Just b
277+ That b -> Just b
278+
279+--TODO: Figure out how to implement this in terms of PatchDMapWithMove rather than duplicating it here
280+-- |Compose patches having the same effect as applying the patches in turn: @'applyAlways' (p <> q) == 'applyAlways' p . 'applyAlways' q@
281+instance Ord k => Monoid (PatchMapWithMove k v) where
282+ mempty = PatchMapWithMove mempty
283+ mappend = (<>)